In recent years, a mobile communication device such as a portable telephone, a portable router, or the like has been downsized. And according to downsizing of the mobile communication device, a built-in antenna used for the mobile communication device is also downsized. Due to downsizing the antenna, it is difficult to realize an antenna with good communication performance. Namely, in order to transmit and receive a radio wave with a frequency allocated for wireless communication, the electrical length of the antenna has to match the wavelength of the radio wave with the frequency allocated for wireless communication. However, in case of downsizing the antenna, it is difficult to get the required electrical length. In particular, in case of further downsizing the antenna, it is difficult for the antenna to perform good communication by using a radio wave with low bandwidth whose wavelength is large. Therefore, the antenna has a problem in which it is difficult to downsize the antenna while maintaining communication performance.
In patent literature 1 (WO2005/029638 A1), there is described a structure in which a feed antenna is configured on a first circuit board and a parasitic antenna is configured on a second circuit board. Further, in patent literature 1, there is described a structure in which the parasitic antenna is coupled to a GND (Ground) part via a coil.
In patent literature 2 (WO2009/147885 A1), there is described a structure in which in a multi-band antenna including a feed element and a parasitic element, an LC resonant circuit is interposed in each of the feed element and the parasitic element.
In patent literature 3 (JP2011-119949 A), there is described a structure in which a feed antenna element is configured on one surface of a circuit board of which a wireless LAN (Local Area Network) card is formed and a parasitic antenna element is configured on the other surface.